1. Field of the Invention
This invention relates generally to vascular devices, and more particularly to a vascular filter that employs an expandable filter to capture particles in the blood stream.
2. Description of the Related Art
A large variety of vascular disorders are currently diagnosed and treated using non-invasive intervention techniques. Examples of such abnormalities are legion, including such conditions as atherosclerosis, arteriosclerosis, cerebral and coronary thrombosis, and aortic aneurysm, to name just a few. The types of vascular intervention techniques used to treat such conditions include, for example, coronary artery by-passes and grafts, aortic aneurism repair, and carotid angioplasty, coronary angioplasty, and intercranial angioplasty with or without the stent placement. Although these procedures are employed in several different parts of the patient's body and involve different medical indications, they share several common attributes. To begin with, each of these procedures, in one form or another, involves the movement of one or more catheter or catheter-like devices through the artery or vein affected by the occlusion, aneurism, or other disorder. Proper catheter positioning requires navigation through often constricted and highly irregular vessels, and is impacted by the stiffness of the catheter tip. Stiffer catheters are more difficult to maneuver. In addition, each of these vascular intervention techniques either creates or is subject to the risk of the movement of emboli downstream from the distal end of the implanted catheter or catheters. Such migrating emboli may be the result of the intentional fragmentation of material within the vessel, such as plaque or a thrombus, or may be the result of dislodged emboli that developed naturally elsewhere in the patient's body.
Migrating emboli can lead to a variety of problematic medical conditions. Depending on the size and origin of the emboli, the patient can develop cardiac valve and vessel occlusion and damage, renal artery occlusion or phlebitis. If the emboli circulate to and lodge in the vascular tree of the head and neck, the result may be ischemic stroke.
Various mechanisms have been developed to capture embolic material dislodged during vascular intervention. One such conventional design consists of a flexible tubular sheath which temporarily encloses one or more wire frames. The wire frames are constructed of a shape memory effect alloy in the super elastic state and are deplorable from the sheath to form two loops about which a filter sack is attached. The wire frames are attached to an elongated wire linkage by a relatively rigid crimp junction. Two disadvantages associated with this conventional design are the propensity of the wire frames to dislodge from the crimp junction and the inherent stiffness of the crimp junction. As noted above, it is desirable for the distal end of any vascular intervention catheter or catheter-like device to be highly flexible at its distal end to facilitate navigation through irregular and narrow vascular passageways. The crimp junction presents a relatively rigid impediment to bending motion of this conventional design.
Another conventional vascular filter device consists of a straight shaped memory wire that is partially positioned within a flexible tube. The wire is folded back upon itself and the two ends thereof are connected proximally to a handle assembly. The middle portion of the wire is crimped. A portion of the wire distal to the crimp is projectable out of the sleeve in the form of a loop to which a filter bag is attached. The loop is expandable and retractable by application of axial force to the two proximal ends of the wire. To deploy the loop, axial compression is applied to the two proximal ends of the wire to force the loop to project from the sleeve. Retraction involves application of axial tension to the proximal ends of the wire to collapse the loop. A disadvantage associated with this conventional design is the fact that the extremely fine portions of the wire must be capable of transmitting compressive force without binding in order for the loop to successfully deploy. With such fine gauge wires undergoing compression, there is the potential for buckling and binding within the lumen of the sleeve.
Another conventional design employs a wire loop that is coupled to the coiled wire of a guiding catheter. The guiding catheter includes a tubular core about which the guide wire is coiled. The wire loop is positioned eccentrically with respect to the tubular core and is connected to the coiled wire by welding. One difficulty associated with this conventional design is the dedicated eccentric positioning of the loop presents a limit on the minimum diameter vessel that may be navigated and requires more vessel flow area that might otherwise be occupied by another instrument. Another disadvantage is the requirement of a welded junction between the wire loop and the coiled guide wire. The integrity of the junction between the coiled wire and the wire loop is critical for the proper operation of this conventional filter as well as the safety of the patient. As the diameters of the parts joined by welding are quite small, the precision and quality of the weld are critical to the successful joining of these two components.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.